The present invention is concerned with detergent compositions in the form of tablets. These tablets may be for the purpose of fabric washing in a laundry washing machine, for dish washing in a mechanical dish washer or for some other cleaning function.
It is desirable that tablets should have adequate mechanical strength when dry, before use, yet disintegrate and disperse/dissolve quickly when added to wash water. It has not proved simple to achieve both properties simultaneously. As more pressure is used when a tablet is compacted, so the tablet density and strength rise, but the speed of disintegration/dissolution when the tablet comes into contact with wash water goes down.
Tablets of detergent composition may be xe2x80x9chomogenousxe2x80x9d tablets in which the entire tablet consists of a single composition compacted into tablet form. However the present invention is concerned with xe2x80x9cheterogenous tabletsxe2x80x9d in which the tablet is subdivided into more than one separate region and is made from more than one composition. Tablets which are xe2x80x9cheterogenousxe2x80x9d in that they are subdivided into two layers have been marketed commercially.
The use of swelling disintegrants to enhance the disintegration rate of one region of a detergent tablet relative to another region was disclosed in our WO 98/55590, wherein a higher concentration of water-insoluble swelling disintegrant in one region compared to another region, caused the former region to dissolve/disperse faster than the latter region.
It has now been found that by making the inner region of a detergent tablet swell to a greater extent than the regions surrounding it, the rate of dissolution/dispersion of the whole tablet can be improved.
Accordingly, the present invention provides a detergent tablet having at least two discrete regions each compacted from particulate composition, wherein a first said region consists of a compacted particulate composition containing swelling disintegrant such that the region increases in volume on contact with water, and in at least one direction through said region is flanked on both sides by one or more other regions which swell to a lesser extent on contact with water than said first region.
It is preferred that the one or more other regions contain a lower concentration of swelling disintegrant than the first region, or no swelling disintegrant at all. The ratio of concentrations of swelling disintegrant between the first region, and the one or more other regions is at least greater than 1:1, preferably greater than 3:1 or even 7:1.
In particular, if the one or more other regions contain the same swelling disintegrant which is in the first region, then the concentration of said swelling disintegrant is lower in the one or more other regions than in the first region.
However, it is also envisaged that the one or more other regions may contain an equal or greater concentration of swelling disintegrant than the first region, but in this case the swelling disintegrant or disintegrants in the one or more other regions will have a lower swelling capacity than the swelling disintegrant in the first region. The ratios of swelling capacity between the first region, and the one or more other regions is at least greater than 1:1, preferably greater than 3:1 or even 7:1.
The invention encompasses a number of tablet forms are these are discussed below.
In one form, the tablet has a pair of opposite faces spaced apart from each other and joined by a peripheral surface of the tablet, wherein said first region provides a first part of a said face and said one or more further regions provide an adjoining part of said face.
The said face may be substantially flat, or the arrangement may be such that the first part of the face is not at the same level as the adjacent part(s), so that there is a step at the junction of the parts. Even if the two parts are at substantially the same level there is likely to be a groove, a slight step or a line in the surface at their junction.
The first part may stand out from the adjacent part of the end face or it may be inset from the adjacent part of the end face.
Preferably the first region is a core which is entirely surrounded by said one or more other regions of the tablet. A single such surrounding region may provide the entire peripheral surface of the tablet and the remainder of the tablet end faces. Other arrangements are conceivable. A region surrounding a core might possibly be split into two or more, such as three, layers, and the core could itself have two layers.
In a preferred arrangement the first region extends through the tablet so as to be visible at both faces, and may be inset from the surrounding part of each face. Another possibility is that such a region could be visible as part of one face yet extend only part way through the tablet, so that subdivision into regions would not be visible at the opposite face of the tablet.
An alternative arrangement is where the first region extends across the whole width of the tablet, such that the first region forms part of the peripheral surface of the tablet.
A region such as a core which provides a first part of a tablet face adjoined or surrounded by a larger second part of the face, is likely to constitute from 10% or 15% up to 35% or 40% of the tablet weight and from 10% or 15% up to 35% or 40% of the area of the tablet face.
One particularly preferred method of making such tablets comprises the steps of:
introducing at least one particulate composition into a mould cavity around a plunger which projects into or through the cavity, followed by driving at least one punch onto the compositions around the plunger in the cavity, thereby compacting them into an outside zone of the tablet
withdrawing the plunger from within the compacted compositions, introducing a further particulate composition into the space vacated by the plunger, and urging at least one plunger against the composition introduced into this space, so as to compact it into an inner zone of the tablet.
There is no need to apply any substantial compaction pressure to the compositions in the outer zone when compacting the further composition, thus allowing the compaction pressure applied to each of the two zones of the tablet to be chosen independently. However, some light pressure may be applied to the (already compacted) compositions in the outer zone to hold them steady while the further composition in the inner zone is compacted.
Preferably the process is carried out using a pair of punches which are relatively movable towards each other within the mould cavity and away from each other, wherein each punch encloses or at least partially surrounds a plunger movable axially relative to the punch. During the first compaction step one or both punches may move. During the second compaction step one or both plungers may move. Conveniently, the particulate compositions of the outer zone would be delivered into the mould cavity above one punch while the plunger associated with that punch project upwardly from it so as to be surrounded by the particulate compositions. If more than one particulate composition is introduced into the outer zone, it is preferred that they are introduced sequentially, so as to produce layers of varying composition. Compaction of the particulate compositions in the outer zone would then be carried out by urging the two punches relatively towards each other, although one may remain stationary relative to the mould cavity if desired. Compaction of the particulate composition in the inner zone would be carried out by urging the two plungers relatively towards each other, although again one may be driven towards the other which remains immobile.
Such a process is preferably carried out using a rotary tableting press in which a rotary table defines a plurality of mould cavities and in which a pair of punches each with a respective axially movable plunger is associated with each mould cavity.
An advantage of the process of this invention is that the core region and surrounding region of the tablet can both be compacted from powder compositions within a single mould cavity. There is no necessity to prefabricate a core region in one mould cavity and somehow position it within another mould cavity. A further advantage is that the tableting pressures applied to each of the compositions can be chosen independently.
The process may lead to tablets in which the compacted further composition provides a part of at least one tablet face which is inset from an adjacent or surrounding part of the tablet face provided by the compositions of the outer zone.
A further form of tablet which is preferred is a tablet with at least three xe2x80x98layersxe2x80x99. The term xe2x80x98layersxe2x80x99 relates to regions of a detergent tablet that are substantially parallel with the compaction faces of the tablet, i.e. those faces to which the compaction force was applied. In such a tablet, the first region is a layer which is flanked on either side by layers which swell to a lesser extent on contact with water than the first region.
Therefore, in a three layer tablet, the first region will be the central layer, whilst the outer two layers will swell to a lesser extent than the central layer on contact with water.
Manufacture of a tablet with at least three layers of differing composition may be carried out by placing a predetermined quantity of one composition in a mould, then adding a second composition on top, followed by third and further compositions, and next driving a die into the mould to cause compaction.
Alternatively, a predetermined quantity of a composition may be placed in a mould and compacted by driving a die into the mould, followed by removing the die, adding a second composition and compacting again, and repeating as necessary.
Tableting machinery able to carry out such operations is known, for example suitable tablet presses are available from Fette and from Korch.
A further form of tablet useful in the invention is one with an xe2x80x98invisiblexe2x80x99 core, which is a region located within the inside of a tablet and which is not visible on the tablet""s periphery. This core is the first region, and is completely surrounded by at least one or more other regions which swell to a lesser extent on contact with water than the first region.
Tablets of the invention may be cylindrical, cuboid or they have more unusual shapes, in particular with rounded, rather than flat, surfaces.
Swelling disintegrants are materials which swell when in contact with water, thus subjecting the compacted tablet composition to internal pressure.
A number of materials are known for use as swelling disintegrants in pharmaceutical tablets and these may be used in detergent tablets of this invention (See Handbook of Pharmaceutical Excipients, 2nd Edition, American Pharmaceutical Association, pp. 141 et seq. (1994)).
Examples include organic materials such as starches, for example, corn, maize, rice and potato starches and starch derivatives, such as Primojel (Trade Mark) carboxymethyl starch and Explotab (Trade Mark) sodium starch glycolate; celluloses and cellulose derivatives, for example, Courlose (Trade Mark) and Nymcel (Trade Mark) sodium carboxymethyl cellulose, Nylin (Trade Mark) cross-linked sodium carboxymethyl cellulose, Ac-di-Sol (Trade Mark) cross-linked modified cellulose, and Hanfloc (Trade Mark) microcrystalline cellulosic fibres; and various synthetic organic polymers, notably cross-linked polvinyl pyrrolidone, for example, Polyplasdone (Trade Mark) Xl or Kollidon (Trade Mark) CL.
Inorganic swelling disintegrants include bentonite clay, and are generally silica based compounds.
A number of materials which may be utilised to make regions of detergent tablets will now be discussed.
Tablets of this invention will generally contain organic surfactant. This will come from one or more of the categories of surfactant used in detergent compositions for fabric washing. These are most usually anionic and nonionic surfactants and mixtures of the two. Amphoteric (including zwitterionic) and less commonly cationic detergents can also be used.
Anionic Surfactant Compounds
Synthetic (i.e. non-soap) anionic surfactants are well known to those skilled in the art. The anionic surfactant may comprise, wholly or predominantly, linear alkyl benzene sulphonate of the formula 
where R is linear alkyl of 8 to 15 carbon atoms and M+ is a solubilising cation, especially sodium.
Primary alkyl sulphate having the formula
ROSO3xe2x88x92M+
in which R is an alkyl or alkenyl chain of 8 to 18 carbon atoms especially 10 to 14 carbon atoms and M+ is a solubilising cation, is also commercially significant as an anionic surfactant and may be used in this invention.
Frequently, such linear alkyl benzene sulphonate or primary alkyl sulphate of the formula above, or a mixture thereof will be the desired non-soap anionic surfactant and may provide 75 to 100 wt % of any anionic non-soap surfactant in the composition.
Examples of other non-soap anionic surfactants include olefin sulphonates; alkane sulphonates; dialkyl sulphosuccinates; and fatty acid ester sulphonates.
One or more soaps of fatty acids may also be included in addition to non-soap anionic surfactant. Examples are sodium soaps derived from the fatty acids from coconut oil, beef tallow, sunflower or hardened rapeseed oil.
Nonionic Surfactant Compounds
Nonionic surfactant compounds include in particular the reaction products of compounds having a hydrophobic group and a reactive hydrogen atom, for example, aliphatic alcohols, acids, amides or alkyl phenols with alkylene oxides, especially ethylene oxide.
Specific nonionic surfactant compounds are alkyl (C8-22) phenol-ethylene oxide condensates, the condensation products of linear or branched aliphatic C8-20 primary or secondary alcohols with ethylene oxide, and products made by condensation of ethylene oxide with the reaction products of propylene oxide and ethylene-diamine.
Especially preferred are the primary and secondary alcohol ethoxylates, especially the C9-11 and C12-15 primary and secondary alcohols ethoxylated with an average of from 3 to 20 moles of ethylene oxide per mole of alcohol.
Amphoteric Surfactants
Amphoteric surfactants which may be used jointly with anionic or nonionic surfactants or both include amphopropionates of the formula: 
where RCO is a acyl group of 8 to 18 carbon atoms, especially coconut acyl.
The category of amphoteric surfactants also includes amine oxides and also zwitterionic surfactants, notably betaines of the general formula 
where R4 is an aliphatic hydrocarbon chain which contains 7 to 17 carbon atoms, R2 and R3 are independently hydrogen, alkyl of 1 to 4 carbon atoms or hydroxyalkyl of 1 to 4 carbon atoms such as CH2OH;
Y is CH2 or of the form CONHCH2CH2CH2 (amidopropyl betaine);
Z is either a COOxe2x88x92 (carboxybetaine), or of the form CHOHCH2SO3xe2x80x94(sulfobetaine or hydroxy sultaine).
Another example of amphoteric surfactant is amine oxide of the formula 
where R1 is C10 to C20 alkyl or alkenyl R2, R3 and R4 are each hydrogen or C1 to C4 alkyl while n is from 1 to 5.
Tablets of this invention will generally include a water-soluble or water-insoluble detergency builder or a mixture of the two.
Water-soluble phosphorus-containing inorganic detergency builders include the sodium and potassium orthophosphates, metaphosphates, pyrophosphates and polyphosphates.
Alkali metal aluminosilicates are strongly favoured as environmentally acceptable water-insoluble builders for fabric washing. Alkali metal (preferably sodium) aluminosilicates may be either crystalline or amorphous or mixtures thereof, having the general formula:
0.8-1.5Na2O.Al2O3. 0.8-6SiO2.xH2O
These materials contain some bound water (indicated as xe2x80x9cxH2Oxe2x80x9d) and are required to have a calcium ion exchange capacity of at least 50 mg CaO/g. The preferred sodium aluminosilicates contain 1.5-3.5 SiO2 units (in the formula above). Both the amorphous and the crystalline materials can be prepared readily by reaction between sodium silicate and sodium aluminate, as amply described in the literature.
Suitable crystalline sodium aluminosilicate ion-exchange detergency builders are described, for example, in GB 1429143 (Procter and Gamble). The preferred sodium aluminosilicates of this type are the well known commercially available zeolites A and X, the zeolite P described and claimed in EP 384070 (Unilever) which is also referred to as zeolite MAP and mixtures thereof. Zeolite MAP is available from Crosfields under their designation Zeolite A24.
Conceivably, water-insoluble detergency builder could be a crystalline layered sodium silicate as described in U.S. Pat. No. 4,664,839.
NaSKS-6 is the trademark for a crystalline layered silicate marketed by Hoechst (commonly abbreviated as xe2x80x9cSKS-6xe2x80x9d). NaSKS-6 has the delta-Na2SiO5 morphology form of layered silicate. It can be prepared by methods such as described in DE-A-3,417,649 and DE-A-3,742,043. Other such layered silicates, which can be used have the general formula NaMSixO2x+1.yH2O wherein M is sodium or hydrogen, x is a number from 1.9 to 4, preferably 2, and y is a number from 0 to 20, preferably 0.
Crystalline layered silicate may be used in the form of granules which also contain citric acid.
Non-phosphorous water-soluble builders may be organic or inorganic. Inorganic builders that may be present include alkali metal (generally sodium) carbonate; while organic builders include polycarboxylate polymers, such as polyacrylates and acrylic/maleic copolymers, monomeric polycarboxylates such as citrates, gluconates, oxydisuccinates, glycerol mono- di- and trisuccinates, carboxymethyloxysuccinates, carboxymethyloxymalonates, dipicolinates and hydroxyethyliminodiacetates.
Alkali metal silicate, particularly sodium ortho-, meta- or disilicate has detergency building properties and may be used in substantial quantity in tablets for machine dishwashing. It is desirably included in smaller quantities in tablets for fabric washing. The presence of such alkali metal silicates may be advantageous in providing protection against the corrosion of metal parts in washing machines, besides providing some detergency building.
Tablet compositions preferably include polycarboxylate polymers, more especially polyacrylates and acrylic/maleic copolymers which can function as builders and also inhibit unwanted deposition onto fabric from the wash liquor.
If a composition is formulated to have low phosphate, the amount of inorganic phosphate builder may be less than 5 wt % of the tablet composition.
Detergent tablets according to the invention may contain a bleach system. This preferably comprises one or more peroxy bleach compounds, for example, inorganic persalts or organic peroxyacids, which may be employed in conjunction with activators to improve bleaching action at low wash temperatures.
Preferred inorganic persalts are sodium perborate monohydrate and tetrahydrate, and sodium percarbonate. These persalts may be provided in coated form, where the coating consists of water-soluble salts.
Bleach activators have been widely disclosed in the art. Preferred examples include peracetic acid precursors, for example tetraacetylethylene diamine (TAED), and perbenzoic acid precursors. The quaternary ammonium and phosphonium bleach activators disclosed in U.S. Pat. No. 4,751,015 and U.S. Pat. No. 4,818,426 (Lever Brothers Company) are also of interest. Another type of bleach activator which may be used, but which is not a bleach precursor, is a transition metal catalyst as disclosed in EP-A-458397, EP-A-458398 and EP-A-549272. A bleach system may also include a bleach stabiliser (heavy metal sequestrant) such as ethylenediamine tetramethylene phosphonate and diethylenetriamine pentamethylene phosphonate.
Tablets of this invention may include further material which functions as a disintegrant, in addition to the swelling disintegrant. It is preferred that further disintegrants are included in the regions with a lower concentration of swelling disintegrant, in order to aid the disintegration and/or dissolution of those regions.
Effervescent Disintegrants
Effervescent disintegrants include weak acids or acid salts, for example, citric acid (preferred), malic acid or tartaric acid, in combination with alkali metal carbonate or bicarbonate; these may suitably be used in an amount of from 1 to 25 wt %, preferably from 5 to 15 wt %. Further examples of acid and carbonate sources and other effervescent systems may be found in Pharmaceutical Dosage Forms: Tablets, Volume 1, 1989, pages 287-291 (Marcel Dekker Inc, ISBN 0-8247-8044-2).
Water-soluble Disintegrants
Such materials include compounds of high water-solubility, a specified form of sodium tripolyphosphate and combinations of these two. Such material may be present as at least 10 or 15% of the composition of a tablet or region thereof, possibly at least 25% up to 50 or 60%, possibly more.
Highly water soluble materials, which are one of the two possibilities are compounds, especially salts, with a solubility at 20xc2x0 C. of at least 50 grams per 100 grams of water. Such materials have been mentioned in our published patent applications including EP-A-711827 and EP-A-838519. A solubility of at least 50 grams per 100 grams of water at 20xc2x0 C. is an exceptionally high solubility: many materials which are classified so as water soluble are less soluble than this.
Some highly water-soluble materials which may be used are listed below, with their solubilities expressed so as grams of solid to form a saturated solution in 100 grams of water at 20xc2x0 C.:
Preferably this highly water soluble material is incorporated so as particles of the material in a substantially pure form (i.e. each such particle contains over 95% by weight of the material). However, the said particles may contain material of such solubility in a mixture with other material, provided that material of the specified solubility provides at least 50% by weight of these particles, better at least 80%.
A particularly preferred material, sodium acetate trihydrate, is normally produced by a crystallisation process, so that the crystallised product contains 3 molecules of water of crystallisation for each sodium and acetate ion pair. Sodium acetate in an incompletely hydrated form, which may be produced by a spray-drying route, can also be used.
Another possibility is that the said particles which promote disintegration are particles containing sodium tripolyphosphate with more than 50% of it (by weight of the particles) in the anhydrous phase I form. Such particles may contain at least 80% by weight tripolyphosphate and possibly at least 95%. Detergent tablets containing such material are the subject of our EP-A-839906.
Sodium tripolyphosphate is very well known so as a sequestering builder in detergent compositions. It exists in a hydrated form and two crystalline anhydrous forms. These are the normal crystalline anhydrous form, known so as phase II which is the low temperature form, and phase I which is stable at high temperature. The conversion of phase II to phase I proceeds fairly rapidly on heating above the transition temperature, which is about 420xc2x0 C., but the reverse reaction is slow. Consequently phase I sodium tripolyphosphate is metastable at ambient temperature.
A process for the manufacture of particles containing a high proportion of the phase I form of sodium tripolyphosphate by spray drying below 420xc2x0 C. is given in U.S. Pat. No. 4536377.
Particles which contain this phase I form will often contain the phase I form of sodium tripolyphosphate so as at least 55% by weight of the tripolyphosphate in the particles. Other forms of sodium tripolyphosphate will usually be present to a lesser extent. Other salts may be included in the particles, although that is not preferred.
Desirably, this sodium tripolyphosphate is partially hydrated. The extent of hydration should be at least 1% by weight of the sodium tripolyphosphate in the particles. It may lie in a range from 2.5 to 4%, or it may be higher, e.g. up to 8%.
Suitable material is commercially available. Suppliers include Rhone-Poulenc, France and Albright and Wilson, UK.
xe2x80x9cRhodiaphos HPA 3.5xe2x80x9d from Rhone-Poulenc has been found particularly suitable. It is a characteristic of this grade of sodium tripolyphosphate that it hydrates very rapidly in a standard Olten test. We have found that it hydrates so as quickly so as anhydrous sodium tripolyphosphate, yet the prehydration appears to be beneficial in avoiding unwanted crystallisation of the hexahydrate when the material comes into contact with water at the time of use.
Tablets of this invention may include an organic water-soluble polymer, serving as a binder when the particles are compacted into tablets. This polymer may be a polycarboxylate included as a supplementary builder, as mentioned earlier. It may be applied as a coating to some or all of the constituent particles prior to compaction.
As taught in our EP-A-522766, such polymers can function to enhance tablet disintegration at the time of use, as well as acting as a binder to enhance tablet strength prior to use.
It is preferred that such a binder material, if present, should melt at a temperature of at least 35xc2x0 C., better at 40xc2x0 C. or above, which is above ambient temperatures in many temperate countries. For use in hotter countries it will be preferred that the melting temperature is somewhat above 40xc2x0 C., so as to be above the ambient temperature.
For convenience the melting temperature of the binder material should be below 80xc2x0 C.
Preferred binder materials are synthetic organic polymers of appropriate melting temperature, especially polyethylene glycol. Polyethylene glycol of average molecular weight 1500 (PEG 1500) melts at 45xc2x0 C. and has proved suitable. Polyethylene glycol of higher molecular weight, notably 4000 or 6000, can also be found.
Other possibilities are polyvinylpyrrolidone, and polyacrylates and water-soluble acrylate copolymers.
The binder may suitably be applied to the particles by spraying, e.g. so as a solution or dispersion. It may be applied to particles which contain organic surfactant. If used, the binder is preferably used in an amount within the range from 0.1 to 10% by weight of the tablet composition, more preferably the amount is at least 1% or even at least 3% by weight of the tablets. Preferably the amount is not over 8% or even 6% by weight unless the binder serves some other additional function.
The detergent tablets of the invention may also contain one of the detergency enzymes well known in the art for their ability to degrade various soils and stains and so aid in their removal. Suitable enzymes include various proteases, cellulases, lipases, amylases, oxidases and mixtures thereof, which are designed to remove a variety of soils and stains from fabrics or from tableware during dishwashing. Cellulases have a fabric softening function also. Detergency enzymes are commonly employed in the form of particles or marumes, optionally with a protective coating, in amount of from about 0.01% often from 0.1% to about 3% by weight of the tablet. A total enzyme content may exceed 3% but is unlikely to exceed 5%. The amount of any one enzyme is likely to lie in a range from 0.01% to 3% by weight of the tablet.
The detergent tablets of the invention may also contain a fluorescer (optical brightener), for example, Tinopal (Trade Mark) DMS or Tinopal CBS available from Ciba-Geigy AG, Basel, Switzerland. Tinopal DMS is disodium 4,4xe2x80x2bis-(2-morpholino-4-anilino-s-triazin-6-ylamino) stilbene disulphonate; and Tinopal CBS is disodium 2,2xe2x80x2-bis-(phenyl-styryl) disulphonate.
An antifoam material is advantageously included, especially if a detergent tablet is primarily intended for use in front-loading drum-type automatic washing machines. Antifoam materials in granular form are described in EP 266863A (Unilever). Such antifoam particles typically comprise a mixture of silicone oil, petroleum jelly, hydrophobic silica and alkyl phosphate so as antifoam active material, sorbed onto a porous absorbed water-soluble carbonate-based inorganic carrier material.
Further ingredients which can optionally be employed in fabric washing detergent tablet of the invention include anti-redeposition agents such so as sodium carboxymethylcellulose, straight-chain polyvinyl pyrrolidone (which can also act as a binder, as mentioned earlier) and the cellulose ethers such as methyl cellulose and ethyl hydroxyethyl cellulose, heavy metal sequestrants such as EDTA; perfumes; fabric softening and/or conditioning agents; soil release polymers and colorants or coloured speckles.
A tablet of this invention intended for fabric washing will generally contain, overall,
at least 5%, better at least 8%, up to not over 50%, possibly not over 30 or 40%, by weight of non-soap organic detergent which is preferably a combination of anionic and nonionic detergents;
at least 15%, better at least 20 or 25%, up to 80%, possibly not over 70 or 60% by weight of one or more detergency builders which may be water-soluble, water-insoluble or a mixture of soluble and insoluble builders;
optionally other ingredients which may amount to at least 10% by weight of the tablet.
The amount of anionic surfactant is likely to be from 5 to 50% by weight of the overall tablet composition while the amount of nonionic surfactant is likely to be from 2% to 40%, better from 4 or 5% up to 30% by weight of the overall tablet. Soap may be included in addition to non-soap anionic surfactant.
A tablet of this invention intended for machine dishwashing, will generally be formulated with a small percentage of nonionic surfactant present such so as 1 to 8% by weight, from 20 to 99% detergency builder, and possibly no anionic detergent at all.
The discrete regions of a tablet may have compositions which lie outside the stated ranges. However, the compositions of regions may well individually conform with the ranges indicated above for a complete tablet of the appropriate character, i.e. machine dishwashing or fabrics washing.
It is likely that each discrete region of a tablet will provide from 5% to 95% of the tablet weight, more preferably from 10 to 80% and likewise from 5 or 10% up to 80% or even 95% of the area of a tablet face.
If a tablet contains peroxygen bleach, the amount of such bleach in the tablet is likely to be from 10% to 25% by weight of the whole tablet composition. Although peroxygen bleaches can be used without a bleach activator, the amount of bleach activator is likely to be from 1 to 10% by weight of the whole tablet; but if the activator is a transition metal catalyst then the amount present is likely to be from 0.01 to 5% by weight of the whole tablet.
The discrete regions of a detergent tablet of this invention, are a matrix of compacted particles. Preferably the particulate mixture of particles, from which each tablet region is compacted, has an average particle size before compaction in the range from 200 to 2000 xcexcm, more preferably from 250 to 1400 xcexcm. Fine particles, smaller than 180 xcexcm or 200 xcexcm may be eliminated by sieving before tableting, if desired, although we have observed that this is not always essential.
While the starting particulate composition may in principle have any bulk density, the present invention is especially relevant to tablets made by compacting powders of relatively high bulk density, because of their greater tendency to exhibit disintegration and dispersion problems. Such tablets have the advantage that, as compared with a tablet derived from a low bulk density powder, a given dose of composition can be presented as a smaller tablet.
Thus the starting particulate composition may suitably have a bulk density of at least 400 g/liter, preferably at least 550 g/liter, and perhaps at least 600 g/liter.
Granular detergent compositions of high bulk density prepared by granulation and densification in a high-speed mixer/granulator, as described and claimed in EP 340013A (Unilever), EP 352135A (Unilever), and EP 425277A (Unilever), or by the continuous granulation/densification processes described and claimed in EP 367339A (Unilever) and EP 390251A (Unilever), are inherently suitable for use in the present invention.
The step of compacting the particles reduces the porosity of the composition. Porosity is conveniently expressed as the percentage of volume which is air.
The air content of a tablet or region of a tablet can be calculated from the volume and weight of the tablet or region, provided the air-free density of the solid content is known. The latter can be measured by compressing a sample of the material under vacuum with a very high applied force, then measuring the weight and volume of the resulting solid.
The percentage air content of a tablet or region of a tablet varies inversely with the pressure applied to compact the composition while the strength of the tablet or region varies with the pressure applied to bring about compaction. Thus the greater the compaction pressure, the stronger the tablet or region becomes but the smaller the air volume within.
The invention may be applied when compacting particulate detergent composition to give tablets with a wide range of porosities. Specifically included among possible porosities is a porosity of up to 38% air volume, e.g. from 10 or 15 better 25% up to 35% air by volume in the tablet.